HydroClim Minnesota - March 2007

A monthly electronic newsletter summarizing Minnesota climate conditions and the resulting impact on water resources.

Distributed on the Wednesday following the first Monday of each month.

State Climatology Office - DNR Waters

compiled 3/6/07 (released one day early)

WHAT HAS HAPPENED

- February 2007 precipitation totals were near average across the northern one third of Minnesota, well above average throughout the southern two thirds of the state. February precipitation topped historical averages by over one inch in many southern Minnesota communities. It was the snowiest February ever in Rochester. When taking into account early-March precipitation values, four-week precipitation totals ending on March 4 exceeded the climatological normal by over two inches in many locales.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/cawap/nwssum/070305.txt )
- for the first three weeks of February, large sections of Minnesota reported little or no snow cover. Conditions abruptly changed during the last weekend of February when a major winter storm plodded through the Upper Midwest and produced some of the heaviest snowfall totals seen in Minnesota in some time. A few locations in southeastern Minnesota reported over two feet of snowfall from February 23 through February 26. The entire state of Minnesota was affected by this winter storm and no location reported a multi-day total of less than six inches. Directly on the heels of the first storm came another powerful winter storm that impacted Minnesota from February 28 through March 2. The second storm left a wide swath of twelve or more inches of snow across much of the southern two thirds of Minnesota and along portions of Minnesota's North Shore. Some eastern and central Minnesota counties reported over 18 inches of snow for the event. Strong winds accompanying the storm led to blizzard conditions in the Duluth area and across areas of western Minnesota.
(see: http://climate.umn.edu/doc/journal/snow070223_26.htm , http://climate.umn.edu/doc/journal/snow070228_070302.htm )
- monthly mean temperatures for February 2007 were well below average throughout Minnesota. Mean temperatures for the month ranged from six to eight degrees below the historical average. The first ten days of the month were the coldest of the winter. Most locations reported temperatures that were 15 to 30 degrees below normal for that period. Many northern Minnesota communities bottomed out at -30 F or colder during the cold snap. Extreme values for February ranged from 54 degrees at Lamberton (Redwood County) on the 21st, to -42 degrees at Embarrass (St. Louis County) on the 4th.
(see: http://climate.umn.edu/cawap/monsum/monsum.asp , http://climate.umn.edu/doc/journal/below_zero_min.htm , http://climate.umn.edu/doc/journal/zero0702.htm )
- the coldest winter temperatures arrived when very little snow was on the ground. Therefore, the frost line plunged rapidly and deeply into the soil during late January and early February. Reports of frozen septic systems and water pipes were common throughout northern Minnesota.

WHERE WE STAND NOW

- the snow depth map to be prepared on Thursday, March 8 will show that nearly all of Minnesota is covered by at least 12 inches of snow. Large areas of southern and central Minnesota, as well as the Lake Superior highlands of northeastern Minnesota, report more than 18 inches of snow on the ground. With the exception of far north central and northeastern counties, Minnesota's snow cover is deeper than the historical median for the date.
(see: http://climate.umn.edu/doc/snowmap.htm )
- much of the snowpack water currently retained on Minnesota's landscape is the result of the late-February and early March snowstorms. Liquid precipitation totals for the two storms were approximately 2.5 inches south of a line that extends from Duluth to Park Rapids to Browns Valley. Some near-shore communities from Duluth to Beaver Bay also received over 2.0 inches of moisture content from the storms. Much of the northern one third of Minnesota reported 0.75 to 1.5 inch of water content. Most of Koochiching county, northern St. Louis county, northern Lake county, and Cook county received less than 0.75 inch of liquid equivalent from the snow events.
- dryness has been entrenched across northern and central Minnesota for nearly ten months. While a welcome site, snowfall from the late-February and early-March winter storms only slightly eased the situation in the far north. Ten-month precipitation totals have deviated negatively from historical averages by more than six inches across much of the northern one half of Minnesota.
(see: http://climate.umn.edu/doc/journal/drought_situation_report_2007.htm )
- the National Drought Mitigation Center (NDMC) - U. S. Drought Monitor released on March 1 continues to indicate that most northern Minnesota counties remain in the "Extreme Drought" or "Severe Drought" categories. Portions of the Red River Valley and central Minnesota are depicted in the "Moderate Drought" classification. An "Abnormally Dry" polygon covers some of west central and central Minnesota. The NDMC index is a blend of science and subjectivity where intensity categories are based on several indicators.
(see: http://www.drought.unl.edu/dm/monitor.html )
- the U.S. Geological Survey reports that stream discharge values (for locations where winter measurements are possible) in northern Minnesota watersheds remain low. Mississippi River flow conditions are very low due to long-term precipitation deficits in the headwaters area.
(see: http://water.usgs.gov/cgi-bin/dailyMainW?state=mn&map_type=weekd )
- soil frost depths are generally between 18 and 42 inches under sod. Frost depths under road surfaces are deeper. Soils in southeastern and south central Minnesota, where snow cover was more persistent this winter, have somewhat shallower frost depths. Frost depths have reached their maximum extent for the season. On average, the soil profile will thaw by late March to early April in the south, early April to mid-April in the north. The soil thaws from both the top and the bottom, leaving a mid-layer lens of frozen soil to be the last to climb above freezing.
(see: http://climate.umn.edu/doc/observatory.htm , http://www.mvp-wc.usace.army.mil/projects/reservoirs.shtml , http://www.mrr.dot.state.mn.us/research/seasonal_load_limits/thawindex/frost_thaw_graphs.asp )

FUTURE PROSPECTS

- the March precipitation outlook from the Climate Prediction Center leans towards above-normal conditions across most of Minnesota. The exception is southwestern Minnesota where the March precipitation outlook is for equal chances of below, near, or above normal conditions. Normal March precipitation ranges from near three quarters of an inch in northwestern Minnesota to around two inches in southern sections of the state. March is a transition month when cold, dry continental air masses are gradually replaced by warmer, moister air on a more frequent basis. This is demonstrated by the fact that March's normal precipitation is 50 percent higher than February's normal precipitation, the greatest percentage increase between any two successive months.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/30day , http://climate.umn.edu/img/normals/precip/precip_norm_03.htm )
- the March temperature outlook offers no strong indications of either above or below normal temperatures in Minnesota. Normal March high temperatures climb from the upper 20's early in the month to the low to mid-40's by month's end. Normal March lows begin the month in the single digits above zero in the far north and mid-teens in the south. By late March, normal lows are in the low 20's in the north, near 30 in the south.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/30day , http://climate.umn.edu/img/normals/temp_norm_adj/temp_norm_adj_03.htm )
- the 90-day precipitation outlook for March through May indicates no significant tendencies away from climatological probabilities across Minnesota. The March through May temperature outlook indicates a tilt towards above-normal conditions throughout the state.
(see: http://www.cpc.ncep.noaa.gov/products/predictions/90day/lead01/index.html )
- the National Weather Service produces long-range probabilistic river stage and discharge outlooks for the Red River, Minnesota River, and Mississippi River basins. These products are part of the National Weather Service's Advanced Hydrologic Prediction Service (AHPS). The North Central River Forecast Center will release its probabilistic Spring Flood Outlook on March 9.
(see: http://www.crh.noaa.gov/ncrfc/ )

NOTES FROM THE AUTHOR

- Northern Minnesota will face many lingering drought issues in 2007. In order to recover rapidly from the 2006 precipitation deficits, spring and summer rainfall totals will need to greatly exceed historical normals. This is possible, but not climatologically likely. The drought was quick to develop, but most likely its impacts will be slow to repair. In keeping with the dry pattern established in 2006, snowfall totals during winter of 2006-2007 have thus far been well short of average. Some drought concerns for the 2007 growing season include:
* increased wildfire risk
* streams dropping below protected flow thresholds after the spring melt runoff
* low lake water levels and associated water access issues
* ground water levels lowering in lagged response to precipitation deficits. Ground water levels will also respond to increased pumping pressures.
* inadequate soil moisture conditions further impacting agriculture, especially forage crops
* inadequate soil moisture conditions further stressing forest communities, making them more vulnerable to pests

NOTES FROM AROUND THE STATE

- none

UPCOMING DATES OF NOTE

- March 9: National Weather Service releases probabilistic outlooks for spring flooding
- March 15: National Weather Service releases 30/90 day temperature and precipitation outlooks